This invention relates to fluid flow control devices, and more particularly, to a solenoid valve or the like wherein the armature of an electromagnet, when energized, urges a valve member onto or off of a valve seat.
Prior art valves are often used in hydraulic device and pressure regulator applications. Using such devices, pressure regulation and flow rate control may be accomplished by controlling the voltage impressed across the electromagnetic winding. In contrast to other prior art are valves wherein the valve was separated from the electromagnet and a mechanical connection had to be first established by a resilient intermediary member, the said other prior art valves were integrally formed. This was true because the valve member formed a spacer between the armature and the yoke. The spacer established an air gap. It is true that this arrangement does not make maximum use of the force of the electromagnet. On the other hand, this method permits positive control of the discharge pressure or of the amount of discharge pressure medium, respectively, because it is by means of the high magnetic reluctance in the air gap that operation in the lower area of the electromagnet's travel/force characteristic is possible. Within the said lower area, the travel/force characteristic curve runs approximately in parallel to the travel axis. This results in always well-defined travel/force intersection points following each other in an almost linear sequence under varying degrees of energization of the electromagnet. This method also avoids the need for a spring between the armature and the valve member, required previously. In the said other valve, the pressure of the valve member bearing upon the valve seat was determined exclusively by the electromagnetic field strength. Thus, if the magnet were suitably designed, the said field strength varied in proportion to the voltage applied to the electromagnet.
When manufacturing the said other valves, there were only two points to be observed regarding the travel/force characteristic:
1. Observance of a given air gap; and PA1 2. Adequate design of the electromagnet.
If the air gap were too small, the valve would operate within the range of an already considerably curved characteristic; and if it were too large, the electromagnetic force would not suffice to control the valve in accord with the given characteristic.
If the design of the electromagnet were inadequate, i.e. if the electromagnetic field were too strong, the valve would operate within the range of an already considerably curved characteristic, and if it were too weak, the electromagnetic forces would not be sufficient to control the valve.
A conventional electromagnetic valve may sometimes be designed without great difficulty; however, difficulties may arise when an attempt is made to fabricate a valve with an air gap defined between very close tolerances.